Resource allocation for d2d discovery transmission

ABSTRACT

The present invention relates to transmitting user equipment for transmitting data to a receiving user equipment over a direct link connection in a communication system. The transmitting user equipment is adapted to request resources for discovery transmission in the communication system and comprises a generating unit configured to generate a resource request message for allocation of resources for discovery transmission. The resource request message includes information on the amount of data to be transmitted and on discovery indication. The transmitting user equipment may further include a transmitting unit configured to transmit to a base station the generated resource request message, and a receiving unit adapted to receive from the base station a resource configuration message allocating the requested resources for discovery transmission.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for performingresource allocation of transmission of discovery information in adevice-to-device communication system. In particular, the presentinvention also relates to a user equipment capable of operating in adevice-to-device communication system and capable of performing themethod of the invention.

TECHNICAL BACKGROUND Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving aradio-access technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. The detailed system requirements are given in 3GPP, TR 25.913(“Requirements for Evolved UTRA and Evolved UTRAN”, www.3gpp.org). InLTE, scalable multiple transmission bandwidths are specified such as1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieve flexiblesystem deployment using a given spectrum. In the downlink, OrthogonalFrequency Division Multiplexing (OFDM) based radio access was adoptedbecause of its inherent immunity to multipath interference (MPI) due toa low symbol rate, the use of a cyclic prefix (CP), and its affinity todifferent transmission bandwidth arrangements. Single-carrier frequencydivision multiple access (SC-FDMA) based radio access was adopted in theuplink, since provisioning of wide area coverage was prioritized overimprovement in the peak data rate considering the restrictedtransmission power of the user equipment (UE). Many key packet radioaccess techniques are employed, including multiple-input multiple-output(MIMO) channel transmission techniques, and a highly efficient controlsignaling structure is achieved in Rel. 8 LTE.

E-UTRAN Architecture

The overall architecture is shown in FIG. 1, and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2. TheE-UTRAN consists of one or more eNodeBs, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe UE. The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control(MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP)layers that include the functionality of user-plane header-compressionand encryption. It also offers Radio Resource Control (RRC)functionality corresponding to the control plane. It performs manyfunctions including radio resource management, admission control,scheduling, enforcement of negotiated uplink Quality of Service (ULQoS), cell information broadcast, ciphering/deciphering of user andcontrol plane data, and compression/decompression of downlink/uplinkuser plane packet headers. The eNodeBs are interconnected with eachother by means of the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (S-GW) bymeans of the S1-U. The S1 interface supports a many-to-many relationbetween MMEs/Serving Gateways and eNodeBs. The SGW routes and forwardsuser data packets, while also acting as the mobility anchor for the userplane during inter-eNB handovers and as the anchor for mobility betweenLTE and other 3GPP technologies (terminating S4 interface and relayingthe traffic between 2G/3G systems and PDN GW). For idle state UEs, theS-GW terminates the downlink data path and triggers paging when downlinkdata arrives for the user equipment. It manages and stores userequipment contexts, e.g., parameters of the IP bearer service, networkinternal routing information. It also performs replication of the usertraffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theS-GW for a user equipment at the initial attach and at time of intra-LTEhandover involving Core Network (CN) node relocation. It is responsiblefor authenticating the user (by interacting with the HSS). TheNon-Access Stratum (NAS) signaling terminates at the MME and it is alsoresponsible for generation and allocation of temporary identities touser equipments. It checks the authorization of the UE to camp on theservice provider's Public Land Mobile Network (PLMN) and enforces userequipment roaming restrictions. The MME is the termination point in thenetwork for ciphering/integrity protection for NAS signaling and handlesthe security key management. Lawful interception of signaling is alsosupported by the MME. The MME also provides the control plane functionfor mobility between LTE and 2G/3G access networks with the S3 interfaceterminating at the MME from the SGSN. The MME also terminates the S6ainterface towards the home HSS for roaming user equipments.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots as shown in FIG. 3, wherein the firstdownlink slot comprises the control channel region (PDCCH region) withinthe first OFDM symbols. Each subframe consists of a given number of OFDMsymbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release8)), wherein each OFDM symbol spans over the entire bandwidth of thecomponent carrier. The OFDM symbols thus each consist of a number ofmodulation symbols transmitted on respective N_(RB) ^(DL)×N_(sc) ^(RB)subcarriers as also shown in FIG. 4.

Assuming a multi-carrier communication system, e.g., employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block is defined as N_(symb) ^(DL) consecutive OFDMsymbols in the time domain and sc consecutive subcarriers in thefrequency domain as exemplified in FIG. 4. In 3GPP LTE (Release 8), aphysical resource block thus consists of N_(symb) ^(DL)×N_(sc) ^(RB)resource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (for further details on the downlinkresource grid, see for example 3GPP TS 36.211, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, version 8.9.0 or 9.0.0, section 6.2, available athttp://www.3gpp.org and incorporated herein by reference).

The term “component carrier” refers to a combination of several resourceblocks. In future releases of LTE, the term “component carrier” is nolonger used; instead, the terminology is changed to “cell”, which refersto a combination of downlink and optionally uplink resources. Thelinking between the carrier frequency of the downlink resources and thecarrier frequency of the uplink resources is indicated in the systeminformation transmitted on the downlink resources.

Further Advancements for LTE (LTE-A)

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the StudyItem description on “Further Advancements for E-UTRA (LTE-Advanced)” wasapproved in the 3GPP. The study item covers technology components to beconsidered for the evolution of E-UTRA, e.g., to fulfill therequirements on IMT-Advanced. Two major technology components which arecurrently under consideration for LTE-A are described in the following.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers (CCs) areaggregated in order to support wider transmission bandwidths up to 100MHz. Several cells in the LTE system are aggregated into one widerchannel in the LTE-Advanced system which is wide enough for 100 MHz,even though these cells in LTE are in different frequency bands. A UEmay simultaneously receive or transmit on one or multiple CCs dependingon its capabilities:

-   -   A Rel-10 UE with reception and/or transmission capabilities for        CA can simultaneously receive and/or transmit on multiple CCs        corresponding to multiple serving cells;    -   A Rel-8/9 UE can receive on a single CC and transmit on a single        CC corresponding to one serving cell only.

Carrier aggregation (CA) is supported for both contiguous andnon-contiguous CCs with each CC limited to a maximum of 110 ResourceBlocks in the frequency domain using the Rel-8/9 numerology.

It is possible to configure a UE to aggregate a different number of CCsoriginating from the same eNB and of possibly different bandwidths inthe UL and the DL.

It is possible to configure a 3GPP LTE-A (Release 10) compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may not be possible to configure amobile terminal with more uplink component carriers than downlinkcomponent carriers.

In a typical TDD deployment, the number of component carriers and thebandwidth of each component carrier in uplink and downlink is the same.Component carriers originating from the same eNodeB need not provide thesame coverage.

Component carriers shall be LTE Rel-8/9 compatible. Nevertheless,existing mechanisms (e.g., barring) may be used to avoid Rel-8/9 UEs tocamp on a component carrier.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time preserve orthogonality of the subcarriers with15 kHz spacing. Depending on the aggregation scenario, the n×300 kHzspacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-M IMO for uplink) at most one transport block percomponent carrier. A transport block and its potential HARQretransmissions need to be mapped on the same component carrier.

The Layer 2 structure with activated carrier aggregation is shown inFIG. 5 and FIG. 6 for the downlink and uplink respectively. Thetransport channels are described between MAC and Layer 1, the logicalchannels are described between MAC and RLC.

When carrier aggregation (CA) is configured, the UE only has one

RRC connection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides theNAS mobility information (e.g., TAI), and at RRC connectionre-establishment/handover, one serving cell provides the security input.This cell is referred to as the Primary Cell (PCell). In the downlink,the carrier corresponding to the PCell is the Downlink Primary ComponentCarrier (DL PCC), while in the uplink it is the Uplink Primary ComponentCarrier (UL PCC).

Depending on UE capabilities, Secondary Cells (SCells) can be configuredto form together with the PCell a set of serving cells. In the downlink,the carrier corresponding to an SCell is a Downlink Secondary ComponentCarrier (DL SCC), while in the uplink it is an Uplink SecondaryComponent Carrier (UL SCC).

The configured set of serving cells for a UE therefore always consistsof one PCell and one or more SCells:

-   -   For each SCell the usage of uplink resources by the UE in        addition to the downlink ones is configurable (the number of DL        SCCs configured is therefore always larger or equal to the        number of UL SCCs and no SCell can be configured for usage of        uplink resources only);    -   From a UE viewpoint, each uplink resource only belongs to one        serving cell;    -   The number of serving cells that can be configured depends on        the aggregation capability of the UE;    -   PCell can only be changed with handover procedure (i.e., with        security key change and RACH procedure);    -   PCell is used for transmission of PUCCH;    -   Unlike SCells, PCell cannot be de-activated;    -   Re-establishment is triggered when the PCell experiences        Rayleigh fading (RLF), not when SCells experience RLF;    -   Non-access stratum (NAS) information is taken from the downlink        PCell.

The configuration and reconfiguration of component carriers can beperformed by RRC. Activation and deactivation is done via MAC controlelements. At intra-LTE handover, RRC can also add, remove, orreconfigure SCells for usage in the target cell. The reconfiguration,addition and removal of SCells can be performed by RRC. At intra-LTEhandover, RRC can also add, remove, or reconfigure SCells for usage withthe target PCell. When adding a new SCell, dedicated RRC signalling isused for sending all required system information of the SCell, i.e.,while in connected mode, UEs need not acquire broadcasted systeminformation directly from the SCells.

When a user equipment is configured with carrier aggregation there isone pair of uplink and downlink component carriers that is alwaysactive. The downlink component carrier of that pair might be alsoreferred to as “DL anchor carrier”. Same applies also for the uplink.

When carrier aggregation is configured, a user equipment may bescheduled over multiple component carriers simultaneously, but at mostone random access procedure shall be ongoing at any time. Cross-carrierscheduling allows the PDCCH of a component carrier to schedule resourceson another component carrier. For this purpose a component carrieridentification field is introduced in the respective DCI formats, calledCIF.

A linking between uplink and downlink component carriers allowsidentifying the uplink component carrier for which the grant applieswhen there is no-cross-carrier scheduling. The linkage of downlinkcomponent carriers to uplink component carrier does not necessarily needto be one to one. In other words, more than one downlink componentcarrier can link to the same uplink component carrier. At the same time,a downlink component carrier can only link to one uplink componentcarrier.

LTE RRC States

The following is mainly describing the two main states in LTE:“RRC_IDLE” and “RRC_CONNECTED”.

In RRC_IDLE the radio is not active, but an ID is assigned and trackedby the network. More specifically, a mobile terminal in RRC_IDLEperforms cell selection and reselection—in other words, it decides onwhich cell to camp. The cell (re)selection process takes into accountthe priority of each applicable frequency of each applicable RadioAccess Technology (RAT), the radio link quality and the cell status(i.e., whether a cell is barred or reserved). An RRC_IDLE mobileterminal monitors a paging channel to detect incoming calls, and alsoacquires system information. The system information mainly consists ofparameters by which the network (E-UTRAN) can control the cell(re)selection process. RRC specifies the control signalling applicablefor a mobile terminal in RRC_IDLE, namely paging and system information.The mobile terminal behavior in RRC_IDLE is specified in TR 25.912,e.g., Chapter 8.4.2 incorporate herein by reference.

In RRC_CONNECTED the mobile terminal has an active radio operation withcontexts in the eNodeB. The E-UTRAN allocates radio resources to themobile terminal to facilitate the transfer of (unicast) data via shareddata channels. To support this operation, the mobile terminal monitorsan associated control channel which is used to indicate the dynamicallocation of the shared transmission resources in time and frequency.The mobile terminal provides the network with reports of its bufferstatus and of the downlink channel quality, as well as neighboring cellmeasurement information to enable E-UTRAN to select the most appropriatecell for the mobile terminal. These measurement reports include cellsusing other frequencies or RATs. The UE also receives systeminformation, consisting mainly of information required to use thetransmission channels. To extend its battery lifetime, a UE inRRC_CONNECTED may be configured with a Discontinuous Reception (DRX)cycle. RRC is the protocol by which the E-UTRAN controls the UE behaviorin RRC_CONNECTED.

Logical and Transport Channels

The MAC layer provides a data transfer service for the RLC layer throughlogical channels. Logical channels are either Control Logical Channelswhich carry control data such as RRC signalling, or Traffic LogicalChannels which carry user plane data. Broadcast Control Channel (BCCH),Paging Control channel (PCCH), Common Control Channel (CCCH), MulticastControl Channel (MCCH) and Dedicated Control Channel (DCCH) are ControlLogical Channels. Dedicated Traffic channel (DTCH) and Multicast TrafficChannel (MTCH) are Traffic Logical Channels.

Data from the MAC layer is exchanged with the physical layer throughTransport Channels. Data is multiplexed into transport channelsdepending on how it is transmitted over the air. Transport channels areclassified as downlink or uplink as follows. Broadcast Channel (BCH),Downlink Shared Channel (DL-SCH), Paging Channel (PCH) and MulticastChannel (MCH) are downlink transport channels, whereas the Uplink SharedChannel (UL-SCH) and the Random Access Channel (RACH) are uplinktransport channels.

A multiplexing is then performed between logical channels and transportchannels in the downlink and uplink respectively.

Layer 1/Layer 2 (L1/L2) Control Signaling

In order to inform the scheduled users about their allocation status,transport format and other data-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length is a multipleof the subframes. The TTI length may be fixed in a service area for allusers, may be different for different users, or may even be dynamic foreach user. Generally, the L1/L2 control signaling needs only betransmitted once per TTI.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which includes resource assignments and other controlinformation for a mobile terminal or groups of UEs. In general, severalPDCCHs can be transmitted in one subframe.

It should be noted that in 3GPP LTE, assignments for uplink datatransmissions, also referred to as uplink scheduling grants or uplinkresource assignments, are also transmitted on the PDCCH.

With respect to scheduling grants, the information sent on the L1/L2control signaling may be separated into the following two categories,Shared Control Information (SCI) carrying Cat 1 information and DownlinkControl Information (DCI) carrying Cat 2/3 information.

Shared Control Information (SCI) carrying Cat 1 Information

The shared control information part of the L1/L2 control signalingcontains information related to the resource allocation (indication).The shared control information typically contains the followinginformation:

-   -   A user identity indicating the user(s) that is/are allocated the        resources.    -   RB allocation information for indicating the resources (Resource        Blocks (RBs)) on which a user(s) is/are allocated. The number of        allocated resource blocks can be dynamic.    -   The duration of assignment (optional), if an assignment over        multiple subframes (or TTIs) is possible.

Depending on the setup of other channels and the setup of the DownlinkControl Information (DCI)—see below—the shared control information mayadditionally contain information such as ACK/NACK for uplinktransmission, uplink scheduling information, information on the DCI(resource, MCS, etc.).

Downlink Control Information (DCI) Carrying Cat 2/3 Information

The downlink control information part of the L1/L2 control signalingcontains information related to the transmission format (Cat 2information) of the data transmitted to a scheduled user indicated bythe Cat 1 information. Moreover, in case of using (Hybrid) ARQ as aretransmission protocol, the Cat 2 information carries HARQ (Cat 3)information. The downlink control information needs only to be decodedby the user scheduled according to Cat 1. The downlink controlinformation typically contains information on:

-   -   Cat 2 information: Modulation scheme, transport-block (payload)        size or coding rate, MIMO (Multiple Input Multiple        Output)-related information, etc. Either the transport-block (or        payload size) or the code rate can be signaled. In any case        these parameters can be calculated from each other by using the        modulation scheme information and the resource information        (number of allocated resource blocks)    -   Cat 3 information: HARQ related information, e.g., hybrid ARQ        process number, redundancy version, retransmission sequence        number

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in its fields. Thedifferent DCI formats that are currently defined for LTE are as followsand described in detail in 3GPP TS 36.212, “Multiplexing and channelcoding”, section 5.3.3.1 (available at http://www.3gpp.org andincorporated herein by reference).

Format 0: DCI Format 0 is used for the transmission of resource grantsfor the PUSCH.

For further information regarding the DCI formats and the particularinformation that is transmitted in the DCI, please refer to thetechnical standard or to LTE—The UMTS Long Term Evolution—From Theory toPractice, Edited by Stefania Sesia, Issam Toufik, Matthew Baker, Chapter9.3, incorporated herein by reference.

Downlink & Uplink Data Transmission

Regarding downlink data transmission, L1/L2 control signaling istransmitted on a separate physical channel (PDCCH), along with thedownlink packet data transmission. This L1/L2 control signalingtypically contains information on:

-   -   The physical resource(s) on which the data is transmitted (e.g.,        subcarriers or subcarrier blocks in case of OFDM, codes in case        of CDMA). This information allows the mobile terminal (receiver)        to identify the resources on which the data is transmitted.    -   When user equipment is configured to have a Carrier Indication        Field (CIF) in the L1/L2 control signaling, this information        identifies the component carrier for which the specific control        signaling information is intended. This enables assignments to        be sent on one component carrier which are intended for another        component carrier (“cross-carrier scheduling”). This other,        cross-scheduled component carrier could be for example a        PDCCH-less component carrier, i.e., the cross-scheduled        component carrier does not carry any L1/L2 control signaling.    -   The Transport Format, which is used for the transmission.

This can be the transport block size of the data (payload size,information bits size), the MCS (Modulation and Coding Scheme) level,the Spectral Efficiency, the code rate, etc. This information (usuallytogether with the resource allocation (e.g., the number of resourceblocks assigned to the user equipment)) allows the user equipment(receiver) to identify the information bit size, the modulation schemeand the code rate in order to start the demodulation, thede-rate-matching and the decoding process. The modulation scheme may besignaled explicitly.

-   -   Hybrid ARQ (HARQ) information:        -   HARQ process number: Allows the user equipment to identify            the hybrid ARQ process on which the data is mapped.        -   Sequence number or new data indicator (NDI): Allows the user            equipment to identify if the transmission is a new packet or            a retransmitted packet. If soft combining is implemented in            the HARQ protocol, the sequence number or new data indicator            together with the HARQ process number enables soft-combining            of the transmissions for a PDU prior to decoding.        -   Redundancy and/or constellation version: Tells the user            equipment, which hybrid ARQ redundancy version is used            (required for de-rate-matching) and/or which modulation            constellation version is used (required for demodulation).    -   UE Identity (UE ID): Tells for which user equipment the L1/L2        control signaling is intended. In typical implementations this        information is used to mask the CRC of the L1/L2 control        signaling in order to prevent other user equipments to read this        information.

To enable an uplink packet data transmission, L1/L2 control signaling istransmitted on the downlink (PDCCH) to tell the user equipment about thetransmission details. This L1/L2 control signaling typically containsinformation on:

-   -   The physical resource(s) on which the user equipment should        transmit the data (e.g., subcarriers or subcarrier blocks in        case of OFDM, codes in case of CDMA).    -   When user equipment is configured to have a Carrier Indication        Field (CIF) in the L1/L2 control signaling, this information        identifies the component carrier for which the specific control        signaling information is intended. This enables assignments to        be sent on one component carrier which are intended for another        component carrier. This other, cross-scheduled component carrier        may be for example a PDCCH-less component carrier, i.e., the        cross-scheduled component carrier does not carry any L1/L2        control signaling.    -   L1/L2 control signaling for uplink grants is sent on the DL        component carrier that is linked with the uplink component        carrier or on one of the several DL component carriers, if        several DL component carriers link to the same UL component        carrier.    -   The Transport Format, the user equipment that should be used for        the transmission. This can be the transport block size of the        data (payload size, information bits size), the MCS (Modulation        and Coding Scheme) level, the Spectral Efficiency, the code        rate, etc. This information (usually together with the resource        allocation (e.g., the number of resource blocks assigned to the        user equipment)) allows the user equipment (transmitter) to pick        the information bit size, the modulation scheme and the code        rate in order to start the modulation, the rate-matching and the        encoding process. In some cases the modulation scheme maybe        signaled explicitly.    -   Hybrid ARQ information:        -   HARQ Process number: Tells the user equipment from which            hybrid ARQ process it should pick the data.        -   Sequence number or new data indicator: Tells the user            equipment to transmit a new packet or to retransmit a            packet. If soft combining is implemented in the HARQ            protocol, the sequence number or new data indicator together            with the HARQ process number enables soft-combining of the            transmissions for a protocol data unit (PDU) prior to            decoding.        -   Redundancy and/or constellation version: Tells the user            equipment which hybrid ARQ redundancy version to use            (required for rate-matching) and/or which modulation            constellation version to use (required for modulation).    -   UE Identity (UE ID): Tells which user equipment should transmit        data. In typical implementations this information is used to        mask the CRC of the L1/L2 control signaling in order to prevent        other user equipments to read this information.

There are several different possibilities of how to exactly transmit theinformation pieces mentioned above in uplink and downlink datatransmission. Moreover, in uplink and downlink, the L1/L2 controlinformation may also contain additional information or may omit some ofthe information. For example:

-   -   HARQ process number may not be needed, i.e., is not signaled, in        case of a synchronous HARQ protocol.    -   A redundancy and/or constellation version may not be needed, and        thus not signaled, if Chase Combining is used (always the same        redundancy and/or constellation version) or if the sequence of        redundancy and/or constellation versions is pre-defined.    -   Power control information may be additionally included in the        control signaling.    -   MIMO related control information, such as, e.g., pre-coding, may        be additionally included in the control signaling.    -   In case of multi-codeword MIMO transmission transport format        and/or HARQ information for multiple code words may be included.

For uplink resource assignments (on the Physical Uplink Shared Channel(PUSCH)) signaled on PDCCH in LTE, the L1/L2 control information doesnot contain a HARQ process number, since a synchronous HARQ protocol isemployed for LTE uplink. The HARQ process to be used for an uplinktransmission is given by the timing. Furthermore, it should be notedthat the redundancy version (RV) information is jointly encoded with thetransport format information, i.e., the RV info is embedded in thetransport format (TF) field. The Transport Format (TF) respectivelymodulation and coding scheme (MCS) field has for example a size of 5bits, which corresponds to 32 entries. 3 TF/MCS table entries arereserved for indicating redundancy versions (RVs) 1, 2 or 3. Theremaining MCS table entries are used to signal the MCS level (TBS)implicitly indicating RV0. The size of the CRC field of the PDCCH is 16bits.

For downlink assignments (PDSCH) signaled on PDCCH in LTE the RedundancyVersion (RV) is signaled separately in a two-bit field. Furthermore themodulation order information is jointly encoded with the transportformat information. Similar to the uplink case there is 5 bit MCS fieldsignaled on PDCCH. 3 of the entries are reserved to signal an explicitmodulation order, providing no Transport format (Transport block) info.For the remaining 29 entries, modulation order and Transport block sizeinfo are signaled.

Uplink Access Scheme for LTE

For Uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and assumed improvedcoverage (higher data rates for a given terminal peak power). Duringeach time interval, Node B assigns users a unique time/frequencyresource for transmitting user data, thereby ensuring intra-cellorthogonality. An orthogonal access in the uplink promises increasedspectral efficiency by eliminating intra-cell interference. Interferencedue to multipath propagation is handled at the base station (Node B),aided by insertion of a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BW_(grant) during one time interval, e.g., asubframe of 0.5 ms, onto which coded information bits are mapped. Itshould be noted that a subframe, also referred to as transmission timeinterval (TTI), is the smallest time interval for user datatransmission. It is however possible to assign a frequency resourceBW_(grant) over a longer time period than one TTI to a user byconcatenation of subframes.

Uplink Scheduling Scheme for LTE

The uplink scheme allows for both scheduled access, i.e., controlled byeNB, and contention-based access.

In case of scheduled access, the UE is allocated a certain frequencyresource for a certain time (i.e., a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access; within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e., when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access the Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines

-   -   which UE(s) that is (are) allowed to transmit,    -   which physical channel resources (frequency),    -   Transport format (Modulation Coding Scheme (MCS)) to be used by        the mobile terminal for transmission.

The allocation information is signaled to the UE via a scheduling grant,sent on the L1/L2 control channel. For simplicity reasons this channelmay be called uplink grant channel in the following. A scheduling grantmessage contains at least information which part of the frequency bandthe UE is allowed to use, the validity period of the grant and thetransport format the UE has to use for the upcoming uplink transmission.The shortest validity period is one subframe. Additional information mayalso be included in the grant message, depending on the selected scheme.Only “per UE” grants are used to grant the right to transmit on theUL-SCH (i.e., there are no “per UE per RB” grants). Therefore, the UEneeds to distribute the allocated resources among the radio bearersaccording to some rules. Unlike in HSUPA there is no UE-based transportformat selection. The eNB decides the transport format based on someinformation, e.g., reported scheduling information and QoS info, and UEhas to follow the selected transport format. In HSUPA the Node B assignsthe maximum uplink resource, and the UE selects accordingly the actualtransport format for the data transmissions.

Since the scheduling of radio resources is the most important functionin a shared channel access network for determining Quality of service,there are a number of requirements that should be fulfilled by the ULscheduling scheme for LTE in order to allow for an efficient QoSmanagement.

-   -   Starvation of low priority services should be avoided;    -   Clear QoS differentiation for radio bearers/services should be        supported by the scheduling scheme;    -   The UL reporting should allow fine granular buffer status        reports (e.g., per radio bearer or per radio bearer group) in        order to allow the eNB scheduler to identify for which Radio        Bearer/service data is to be sent;    -   It should be possible to make clear QoS differentiation between        services of different users;    -   It should be possible to provide a minimum bit rate per radio        bearer.

As can be seen from the above list, one essential aspect of the LTEscheduling scheme is to provide mechanisms with which the operator cancontrol the partitioning of its aggregated cell capacity between theradio bearers of the different QoS classes. The QoS class of a radiobearer is identified by the QoS profile of the corresponding SAE bearersignalled from AGW to eNB as described before. An operator can thenallocate a certain amount of its aggregated cell capacity to theaggregated traffic associated with radio bearers of a certain QoS class.The main goal of employing this class-based approach is to be able todifferentiate the treatment of packets depending on the QoS class theybelong to.

Buffer Status Reporting/Scheduling Request Procedure for UplinkScheduling

The usual mode of scheduling is dynamic scheduling, by means of downlinkassignment messages for the allocation of downlink transmissionresources and uplink grant messages for the allocation of uplinktransmission resources; these are usually valid for specific singlesubframes. They are transmitted on the PDCCH using C-RNTI of the UE asalready mentioned before. Dynamic scheduling is efficient for servicestypes, in which the traffic is bursty and dynamic in rate, such as TCP.

In addition to the dynamic scheduling, a persistent scheduling isdefined, which enables radio resources to be semi-statically configuredand allocated to a UE for a longer time period than one subframe, thusavoiding the need for specific downlink assignment messages or uplinkgrant messages over the PDCCH for each subframe. Persistent schedulingis useful for services such as VoIP for which the data packets aresmall, periodic and semi-static in size. Thus, the overhead of the PDCCHis significantly reduced compared to the case of dynamic scheduling.

Buffer status reports (BSR) from the UE to the eNodeB are used to assistthe eNodeB in allocating uplink resources, i.e., uplink scheduling. Forthe downlink case, the eNB scheduler is obviously aware of the amount ofdata to be delivered to each UE; however, for the uplink direction,since scheduling decisions are done at the eNB and the buffer for thedata is in the UE, BSRs have to be sent from the UE to the eNB in orderto indicate the amount of data that needs to be transmitted over theUL-SCH.

There are basically two types of Buffer Status Report MAC controlelements (BSR) defined for LTE: a long BSR (with four buffer size fieldscorresponding to LCG IDs #0-3) or a short BSR (with one LCG ID field andone corresponding buffer size field). The buffer size field indicatesthe total amount of data available across all logical channels of alogical channel group, and is indicated in number of bytes encoded as anindex of different buffer size levels (see also 3GPP TS 36.321 v 10.5.0Chapter 6.1.3.1, incorporated herewith by reference). In addition, thereis a further type of Buffer Status Report, for use of truncated data,where the Buffer Status Report is 2 bytes long.

Which one of either the short or the long BSR is transmitted by the UEdepends on the available transmission resources in a transport block, onhow many groups of logical channels have non-empty buffers, and onwhether a specific event is triggered at the UE. The long BSR reportsthe amount of data for four logical channel groups, whereas the shortBSR indicates the amount of data buffered for only the highest logicalchannel group.

The reason for introducing the logical channel group concept is thateven though the UE may have more than four logical channels configured,reporting the buffer status for each individual logical channel wouldcause too much signaling overhead. Therefore, the eNB assigns eachlogical channel to a logical channel group; preferably, logical channelswith same/similar QoS requirements should be allocated within the samelogical channel group.

A BSR may be triggered, as an example, for the following events:

-   -   Whenever data arrives for a logical channel, which has a higher        priority than the logical channels whose buffer are non-empty;    -   Whenever data becomes available for any logical channel, when        there was previously no data available for transmission;    -   Whenever the retransmission BSR time expires;    -   Whenever periodic BSR reporting is due, i.e., periodic BSR timer        expires;    -   Whenever there is a spare space in a transport block which can        accommodate a BSR.

In order to be robust against transmission failures, there is a BSRretransmission mechanism defined for LTE; the retransmission BSR timeris started or restarted whenever an uplink grant is restarted. If nouplink grant is received before the retransmission BSR timer expires,another BSR is triggered by the UE.

If the UE has no uplink resources allocated for including a BSR in thetransport block (TB) when a BSR is triggered the UE sends a schedulingrequest (SR) on the Physical Uplink Control Channel (PUCCH), ifconfigured. For the case that there are no D-SR (dedicated Schedulingrequest) resources on PUCCH configured, the UE will start the RandomAccess Procedure (RACH procedure) in order to request UL-SCH resourcesfor transmission the BSR info to eNB. However it should be noted thatthe UE will not trigger SR transmission for the case that a periodic BSRis to be transmitted.

Furthermore an enhancement to the SR transmission has been introducedfor a specific scheduling mode where resources are persistentlyallocated with a defined periodicity in order to save L1/L2 controlsignalling overhead for transmission grants, which is referred to assemi-persistent scheduling (SPS). One example for a service, which hasbeen mainly considered for semi-persistent scheduling, is VoIP. Every 20ms a VoIP packet is generated at the Codec during a talk-spurt.Therefore eNB can allocate uplink or respectively downlink resourcepersistently every 20 ms, which could be then used for the transmissionof VoIP packets. In general SPS is beneficial for services withpredictable traffic behavior, i.e., constant bit rate, packet arrivaltime is periodic. For the case that SPS is configured for the uplinkdirection, the eNB can turn off SR triggering/transmission for certainconfigured logical channels, i.e., BSR triggering due to data arrival onthose specific configured logical channels will not trigger an SR. Themotivation for such kind of enhancements is that reporting an SR forthose logical channels which will use the semi-persistently allocatedresources (logical channels which carry VoIP packets) is of no value foreNB scheduling, and hence should be avoided.

More detailed information with regard to BSR and in particular thetriggering of same is explained in 3GPP TS 36.321 V10.5 in Chapter 5.4.5incorporated herewith by reference.

Logical Channel Prioritization

The UE has an uplink rate control function which manages the sharing ofuplink resources between radio bearers. This uplink rate controlfunction is also referred to as logical channel prioritization procedurein the following. The Logical Channel Prioritization (LCP) procedure isapplied when a new transmission is performed, i.e., a Transport blockneeds to be generated. One proposal for assigning capacity has been toassign resources to each bearer, in priority order, until each hasreceived an allocation equivalent to the minimum data rate for thatbearer, after which any additional capacity is assigned to bearers in,for example, priority order.

As will become evident from the description of the LCP procedure givenbelow, the implementation of the LCP procedure residing in the UE isbased on the token bucket model, which is well known in the IP world.The basic functionality of this model is as follows. Periodically at agiven rate, a token, which represents the right to transmit a quantityof data, is added to the bucket. When the UE is granted resources, it isallowed to transmit data up to the amount represented by the number oftokens in the bucket. When transmitting data the UE removes the numberof tokens equivalent to the quantity of transmitted data. In case thebucket is full, any further tokens are discarded. For the addition oftokens it could be assumed that the period of the repetition of thisprocess would be every TTI, but it could be easily lengthened such thata token is only added every second. Basically instead of every 1 ms atoken is added to the bucket, 1000 tokens could be added every second.In the following, the logical channel prioritization procedure which isused in Rel-8 is described.

More detailed information with regard to the LCP procedure is explainedin 3GPP TS 36.321 V8 in Chapter 5.4.3.1, incorporated herewith byreference.

RRC controls the scheduling of uplink data by signalling for eachlogical channel: priority where an increasing priority value indicates alower priority level, prioritisedBitRate which sets the Prioritized BitRate (PBR), and bucketSizeDuration which sets the Bucket Size Duration(BSD). The idea behind prioritized bit rate is to support for eachbearer, including low priority non-GBR bearers, a minimum bit rate inorder to avoid a potential starvation. Each bearer should at least getenough resources in order to achieve the prioritized bit rate (PRB).

The UE shall maintain a variable Bj for each logical channel j. Bj shallbe initialized to zero when the related logical channel is established,and incremented by the product PBR×TTI duration for each TTI, where PBRis Prioritized Bit Rate of logical channel j. However, the value of Bjcan never exceed the bucket size, and if the value of Bj is larger thanthe bucket size of logical channel j, it shall be set to the bucketsize. The bucket size of a logical channel is equal to PBR×BSD, wherePBR and BSD are configured by upper layers.

The UE shall perform the following Logical Channel Prioritizationprocedure when a new transmission is performed:

-   -   The UE shall allocate resources to the logical channels in the        following steps:    -   Step 1: All the logical channels with Bj>0 are allocated        resources in a decreasing priority order. If the PBR of a radio        bearer is set to “infinity”, the UE shall allocate resources for        all the data that is available for transmission on the radio        bearer before meeting the PBR of the lower priority radio        bearer(s);    -   Step 2: the UE shall decrement Bj by the total size of MAC SDUs        served to logical channel j in Step 1;

It has to be noted at this point that the value of Bj can be negative.

-   -   Step 3: if any resources remain, all the logical channels are        served in a strict decreasing priority order (regardless of the        value of Bj) until either the data for that logical channel or        the UL grant is exhausted, whichever comes first. Logical        channels configured with equal priority should be served        equally.    -   The UE shall also follow the rules below during the scheduling        procedures above:    -   the UE should not segment an RLC SDU (or partially transmitted        SDU or retransmitted RLC PDU) if the whole SDU (or partially        transmitted SDU or retransmitted RLC PDU) fits into the        remaining resources;    -   if the UE segments an RLC SDU from the logical channel, it shall        maximize the size of the segment to fill the grant as much as        possible;    -   UE should maximize the transmission of data.

For the Logical Channel Prioritization procedure, the UE shall take intoaccount the following relative priority in decreasing order:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for PHR;    -   data from any Logical Channel, except data from UL-CCCH;    -   MAC control element for BSR included for padding.

For the case of carrier aggregation, which is described in a latersection, when the UE is requested to transmit multiple MAC PDUs in oneTTI, steps 1 to 3 and the associated rules may be applied either to eachgrant independently or to the sum of the capacities of the grants. Alsothe order in which the grants are processed is left up to UEimplementation. It is up to the UE implementation to decide in which MACPDU a MAC control element is included when UE is requested to transmitmultiple MAC PDUs in one TTI.

Uplink Power Control

Uplink transmission power control in a mobile communication systemserves an important purpose: it balances the need for sufficienttransmitted energy per bit to achieve the required Quality-of-Service(QoS), against the needs to minimize interference to other users of thesystem and to maximize the battery life of the mobile terminal. Inachieving this purpose, the role of the Power Control (PC) becomesdecisive to provide the required SINR, while controlling at the sametime the interference caused to neighboring cells. The idea of classicPC schemes in uplink is that all users are received with the same SINR,which is known as full compensation. As an alternative, 3GPP has adoptedfor LTE the use of Fractional Power Control (FPC). This newfunctionality makes users with a higher path loss operate at a lowerSINR requirement so that they will more likely generate lessinterference to neighboring cells.

Detailed power control formulae are specified in LTE for the PhysicalUplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH)and the Sounding Reference Signals (SRSs) (section 5.1 in TS 36.213).The formula for each of these uplink signals follows the same basicprinciples; in all cases they can be considered as a summation of twomain terms: a basic open-loop operating point derived from static orsemi-static parameters signalled by the eNodeB, and a dynamic offsetupdated from subframe to subframe.

The basic open-loop operating point for the transmit power per resourceblock depends on a number of factors including the inter-cellinterference and cell load. It can be further broken down into twocomponents, a semi-static base level P0, further comprised of a commonpower level for all UEs in the cell (measured in dBm) and a UE-specificoffset, and an open-loop path loss compensation component. The dynamicoffset part of the power per resource block can also be further brokendown into two components, a component dependent on the used MCS andexplicit Transmitter Power Control (TPC) commands.

The MCS-dependent component (referred to in the LTE specifications asΔ_(TF), where TF stands for “Transport Format”) allows the transmittedpower per RB to be adapted according to the transmitted information datarate.

The other component of the dynamic offset is the UE-specific TPCcommands. These can operate in two different modes: accumulative TPCcommands (available for PUSCH, PUCCH and SRS) and absolute TPC commands(available for PUSCH only). For the PUSCH, the switch between these twomodes is configured semi-statically for each UE by RRC signalling—i.e.,the mode cannot be changed dynamically. With the accumulative TPCcommands, each TPC command signals a power step relative to the previouslevel.

Power Headroom Reporting

In order to assist the eNodeB to schedule the uplink transmissionresources to different UEs in an appropriate way, it is important thatthe UE can report its available power headroom to eNodeB.

The eNodeB can use the power headroom reports to determine how much moreuplink bandwidth per subframe a UE is capable of using. This helps toavoid allocating uplink transmission resources to UEs which are unableto use them, in order to avoid a waste of resources.

The range of the power headroom report is from +40 to −23 dB. Thenegative part of the range enables the UE to signal to the eNodeB theextent to which it has received an UL grant which would require moretransmission power than the UE has available. This would enable theeNodeB to reduce the size of a subsequent grant, thus freeing uptransmission resources to allocate to other UEs.

A power headroom report can only be sent in subframes in which a UE hasan UL grant. The report relates to the subframe in which it is sent. Anumber of criteria are defined to trigger a power headroom report. Theseinclude:

-   -   A significant change in estimated path loss since the last power        headroom report,    -   More than a configured time has elapsed since the previous power        headroom report,    -   More than a configured number of closed-loop TPC commands have        been implemented by the UE.

The eNodeB can configure parameters to control each of these triggersdepending on the system loading and the requirements of its schedulingalgorithm. To be more specific, RRC controls power headroom reporting byconfiguring the two timers periodicPHR-Timer and prohibitPHR-Timer, andby signalling dl-PathlossChange, which sets the change in measureddownlink path loss to trigger a power headroom report.

The power headroom report is send as a MAC Control Element. It consistsof a single octet where the two highest bits are reserved and the sixlowest bits represent the dB values mentioned above in 1 dB steps. Thestructure of the MAC Control Element is shown in FIG. 7.

The UE power headroom PH valid for subframe i is defined by:

PH(i)=P _(CMAX)−{10 log₁₀(M _(PUSCH)(i))+P _(O_PUSCH)(j)+α(j)·PL+Δ_(TF)(i)+ƒ(i)} [dB]

The power headroom shall be rounded to the closest value in the range[40; −23] dB with steps of 1 dB.

P_(cmax), the maximum UE Transmission power (Tx power) is a value chosenby the UE in the given range of P_(CMAX_L) and P_(CMAX_H).

P _(CMAX_L) ≤P _(CMAX) ≤P _(CMAX_H), where

P _(CMAX_L)=MIN{P _(EMAX) −ΔT _(C) ,P _(PowerClass) −MPR−A-MPR−ΔT _(C)},and

P _(CMAX_H)=MIN{P _(EMAX) ,P _(PowerClass)},

and where P_(EMAX) is the value signalled by the network.

MPR is a power reduction value used to control the adjacent channelleakage power ratio (ACLR) associated with the various modulationschemes and the transmission bandwidth.

A-MPR is the additional maximum power reduction. It is band-specific andit is applied when configured by the network. Therefore, P_(cmax) isUE-implementation-specific and hence not known by eNB.

More detailed information with regard to ΔT_(C) is specified in 3GPP TS36.101, Vers. 12.0.0, section 6.2.5, incorporated herein by reference.

LTE Device-to-Device (D2D) Proximity Services

Proximity-based applications and services represent an emergingsocial-technological trend. The identified areas include servicesrelated to commercial services and Public Safety that would be ofinterest to operators and users. The introduction of a ProximityServices (ProSe) capability in LTE would allow the 3GPP industry toserve this developing market, and will, at the same time, serve theurgent needs of several Public Safety communities that are jointlycommitted to LTE.

Device-to-Device (D2D) communication is a technology component forLTE-rel. 12. The Device-to-Device (D2D) communication technology allowsD2D as an underlay to the cellular network to increase the spectralefficiency. For example, if the cellular network is LTE, all datacarrying physical channels use SC-FDMA for D2D signalling. In D2Dcommunication, user equipments (UEs) transmit data signals to each otherover a direct link using the cellular resources instead of through theBase Station. A possible scenario in a D2D compatible communicationsystem is shown in FIG. 9.

D2D Communication in LTE

The “D2D communication in LTE” is focusing on two areas: Discovery andCommunication, whereas this invention is mostly related to the Discoverypart.

Device-to-Device (D2D) communication is a technology component forLTE-A. In D2D communication, UEs transmit data signals to each otherover a direct link using the cellular resources instead of through theBS. D2D users communicate directly while remaining controlled under theBS, i.e., at least when being in coverage of an eNB. Therefore D2D canimprove system performances by reusing cellular resources.

It is assumed that D2D operates in uplink LTE spectrum (in the case ofFDD) or uplink subframes of the cell giving coverage (in case of TDDexcept when out of coverage). Furthermore D2D transmission/receptiondoes not use full duplex on a given carrier. From individual UEperspective, on a given carrier D2D signal reception and LTE uplinktransmission do not use full duplex, i.e., no simultaneous D2D signalreception and LTE UL transmission is possible.

In D2D communication when UE1 has a role of transmission (transmittinguser equipment), UE1 sends data and UE2 (receiving user equipment)receives it. UE1 and UE2 can change their transmission and receptionrole. The transmission from UE1 can be received by one or more UEs likeUE2.

With respect to the user plane protocols, in the following the contentof the agreement from D2D communication perspective is reported (3GPP TR36.843 vers. 12.0.0 section 9.2, incorporated herein by reference):

-   -   PDCP:        -   1: M D2D broadcast communication data (i.e., IP packets)            should be handled as the normal user-plane data.        -   Header-compression/decompression in PDCP is applicable for            1: M D2D broadcast communication.            -   U-Mode is used for header compression in PDCP for D2D                broadcast operation for public safety.    -   RLC:        -   RLC UM is used for 1: M D2D broadcast communication.        -   Segmentation and Re-assembly is supported on L2 by RLC UM.        -   A receiving UE needs to maintain at least one RLC UM entity            per transmitting peer UE.        -   An RLC UM receiver entity does not need to be configured            prior to reception of the first RLC UM data unit.        -   So far no need has been identified for RLC AM or RLC TM for            D2D communication for user plane data transmission.    -   MAC:        -   No HARQ feedback is assumed for 1: M D2D broadcast            communication.        -   The receiving UE needs to know a source ID in order to            identify the receiver RLC UM entity.        -   The MAC header comprises a L2 target ID which allows            filtering out packets at MAC layer.        -   The L2 target ID may be a broadcast, group cast or unicast            address.            -   L2 Groupcast/Unicast: A L2 target ID carried in the MAC                header would allow discarding a received RLC UM PDU even                before delivering it to the RLC receiver entity.            -   L2 Broadcast: A receiving UE would process all received                RLC PDUs from all transmitters and aim to re-assemble                and deliver IP packets to upper layers.        -   MAC subheader contains LCIDs (to differentiate multiple            logical channels).        -   At least Multiplexing/de-multiplexing, priority handling and            padding are useful for D2D.

Resource Allocation

The resource allocation for D2D communication is under discussion and isdescribed in its present form in 3GPP TR 36.843, version 12.0.0, section9.2.3, incorporated herein by reference.

From the perspective of a transmitting UE, a UE can operate in two modesfor resource allocation:

-   -   Mode 1: eNodeB or Release-10 relay node schedules the exact        resources used by a UE to transmit direct data and direct        control information;    -   Mode 2: a UE on its own selects resources from resource pools to        transmit direct data and direct control information.

D2D communication capable UE shall support at least Mode 1 forin-coverage. D2D communication capable UE shall support Mode 2 for atleast edge-of-coverage and/or out-of-coverage.

UEs in-coverage and out-of-coverage need to be aware of a resource pool(time/frequency) for D2D communication reception.

All UEs (Mode 1 (“scheduled”) and Mode 2 (“autonomous”)) are providedwith a resource pool (time and frequency) in which they attempt toreceive scheduling assignments.

In Mode 1, a UE requests transmission resources from an eNodeB. TheeNodeB schedules transmission resources for transmission of schedulingassignment(s) and data.

-   -   The UE sends a scheduling request (D-SR or RA) to the eNodeB        followed by a BSR, based on which the eNodeB can determine that        the UE intends to perform a D2D transmission as well as the        required amount resources.    -   In Mode 1, the UE needs to be RRC Connected in order to transmit        D2D communication.

For Mode 2, UEs are provided with a resource pool (time and frequency)from which they choose resources for transmitting D2D communication.

FIG. 8 schematically illustrates the Overlay (LTE) and the Underlay(D2D) transmission and/or reception resources. The eNodeB controlswhether the UE may apply Mode 1 or Mode 2 transmission. Once the UEknows its resources where it can transmit (or receive) D2Dcommunication, it uses the corresponding resources only for thecorresponding transmission/reception. In the example of FIG. 8, the D2Dsubframes will only be used to receive or transmit the D2D signals.Since the UE as a D2D device would operate in Half Duplex mode, it caneither receive or transmit the D2D signals at any point of time.Similarly, in the same figure, the other subframes can be used for LTE(overlay) transmissions and/or reception.

D2D discovery is the procedure/process of identifying other D2D capableand interested devices in the vicinity. For this purpose, the D2Ddevices that want to be discovered would send some discovery signals (oncertain network resources) and the receiving UE interested in the saiddiscovery signal will come to know of such transmitting D2D devices. Ch.8 of 3GPP TS 36.843 describes the available details of D2D Discoverymechanisms.

D2D Discovery

ProSe (Proximity based Services) Direct Discovery is defined as theprocedure used by the ProSe-enabled UE to discover other ProSe-enabledUE(s) in its proximity using E-UTRA direct radio signals via the PC5interface. FIG. 10 schematically illustrates a PC5 interface fordevice-to-device direct discovery.

Upper layer handles authorization for announcement and monitoring ofdiscovery information. For the purpose, UEs have to exchange predefinedsignals, referred to as discovery signals. By checking discovery signalsperiodically, a UE maintains a list of proximity UEs in order toestablish communication link when it is needed. Discovery signals shouldbe detected reliably, even in low Signal-to-Noise Ratio (SNR)environments. To allow discovery signals to be transmitted periodically,resources for Discovery signals should be assigned.

There are two types of ProSe Direct Discovery: open and restricted. Openis the case where there is no explicit permission that is needed fromthe UE being discovered, whereas restricted discovery only takes placewith explicit permission from the UE that is being discovered.

ProSe Direct Discovery can be a standalone service enabler in adiscovering UE, which enables the discovering UE to use information froma discovered UE for certain applications. As an example, the informationtransmitted in ProSe Direct Discovery may be “find a taxi nearby”, “findme a coffee shop”, “find me the nearest police station” and the like.Through ProSe Direct Discovery a discovery UE can retrieve neededinformation. Additionally, depending on the information obtained, ProSeDirect Discovery can be used for subsequent actions in thetelecommunication system, such as, for example, initiating ProSe DirectCommunication.

ProSe Direct Discovery Models

ProSe Direct Discovery is based on several discovery models. The modelsfor ProSe Direct Discovery are defined in 3GPP TS 23.303 V12.0.0,section 5.3.1.2 which is enclosed herein by reference:

Model A (“I am Here”)

Model A is also indicated as “I am here”, since the announcing UEbroadcasts information about itself, such as its ProSe ApplicationIdentities or ProSe UE Identities in the discovery message, therebyidentifying itself and communicating to the other parties of thecommunication system that it is available.

According to Model A two roles for ProSe-enabled UEs that areparticipating in ProSe Direct Discovery are defined. ProSe-enabled UEcan have the function of Announcing UE and Monitoring UE. An announcingUE announces certain information that could be used by UEs in proximitythat have permission to discover. A Monitoring UE monitors certaininformation of interest in proximity of announcing UEs.

In this model the announcing UE broadcasts discovery messages atpre-defined discovery intervals and the monitoring UEs that areinterested in these messages read them and process them.

Model B (“Who is There?”/“are You There?”)

Model B is equivalent to “who is there/are you there” since thediscoverer UE transmits information about other UEs that it would liketo receive responses from. The transmitted information can be, forexample, about a ProSe Application Identity corresponding to a group.The members of the group can respond to said transmitted information.

According to this model two roles for the ProSe-enabled UEs that areparticipating in ProSe Direct Discovery are defined: discoverer UE anddiscoveree UE. The discoverer UE transmits a request containing certaininformation about what it is interested to discover. On the other hand,the discoveree UE receives the request message can respond with someinformation related to the discoverer's request.

The content of discovery information is transparent to Access Stratum(AS), which does not know the content of discovery information. Thus, nodistinction is made in the Access Stratum between the various ProSeDirect Discovery models and types of ProSe Direct Discovery. The ProSeProtocol ensures that it delivers only valid discovery information to ASfor announcement.

The UE can participate in announcing and monitoring of discoveryinformation in both RRC_IDLE and RRC_CONNECTED state as per eNBconfiguration. The UE announces and monitors its discovery informationsubject to the half-duplex constraints.

Types of Discovery

D2D communication may either be network-controlled, where the operatormanages the switching between direct transmissions (D2D) andconventional cellular links, or the direct links may be managed by thedevices without operator control. D2D allows combininginfrastructure-mode and ad hoc communication.

Generally device discovery is needed periodically. Further D2D devicesutilize a discovery message signalling protocol to perform devicediscovery. For example, a D2D-enabled UE can transmit its discoverymessage and another D2D enabled UE receives this discovery message andcan use the information to establish a communication link. An advantageof a hybrid network is that if D2D devices are also in communicationrange of network infrastructure, a network entity like eNB canadditionally assist in the transmission or configuration of discoverymessages. Coordination/control by the eNB in the transmission orconfiguration of discovery messages is also important to ensure that D2Dmessaging does not create interference to the cellular trafficcontrolled by the eNB. Additionally, even if some of the devices areoutside of the network coverage range, in-coverage devices can assist inthe ad-hoc discovery protocol.

At least the following two types of discovery procedure are defined forthe purpose of terminology definition used further in the description.

-   -   Type 1: A resource allocation procedure where resources for        announcing of discovery information are allocated on a        non-UE-specific basis, further characterized by:        -   The eNB provides the UE(s) with the resource pool            configuration used for announcing of discovery information.            The configuration may be signalled in SIB.        -   The UE autonomously selects radio resource(s) from the            indicated resource pool and can announce discovery            information.        -   The UE can announce discovery information on a randomly            selected discovery resource during each discovery period.        -   Type 2: A resource allocation procedure where resources for            announcing of discovery information are allocated on a per            UE-specific basis, further characterized by:            -   The UE in RRC_CONNECTED may request resource(s) for                announcing of discovery information from the eNB via                RRC. The eNB assigns resource(s) via RRC.            -   The resources are allocated within the resource pool                that is configured in UEs for monitoring.

The resources are according to the type 2 procedure for exampleallocated semi-persistently allocated for discovery signal transmission.

In the case UEs are in RRC_IDLE modus, the eNB may select one of thefollowing options:

-   -   The eNB may provide a Type 1 resource pool for discovery        information announcement in SIB. UEs that are authorized for        ProSe Direct Discovery use these resources for announcing        discovery information in RRC_IDLE.    -   The eNB may indicate in SIB that it supports D2D but does not        provide resources for discovery information announcement. UEs        need to enter RRC Connected in order to request D2D resources        for discovery information announcement.

For UEs in RRC_CONNECTED status, a UE authorized to perform ProSe DirectDiscovery announcement indicates to the eNB that it wants to perform D2Ddiscovery announcement. Then, the eNB validates whether the UE isauthorized for ProSe Direct Discovery announcement using the UE contextreceived from MME.

The eNB may configure the UE to use a Type 1 resource pool or dedicatedType 2 resources for discovery information announcement via dedicatedRRC signalling (or no resource). The resources allocated by the eNB arevalid until a) the eNB de-configures the resource(s) by RRC signalling,or b) the UE enters IDLE.

Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type2 discovery resource pools as authorized. The eNB provides the resourcepool configuration used for discovery information monitoring in SIB. TheSIB may contain discovery resources used for announcing in neighborcells as well.

Radio Protocol Architecture

FIG. 11 schematically illustrates a Radio Protocol Stack (AS) for ProSeDirect Discovery.

The AS layer interfaces with upper layer (ProSe Protocol). Accordingly,the MAC layer receives the discovery information from the upper layer(ProSe Protocol). In this context, the IP layer is not used fortransmitting the discovery information. Further, the AS layer has ascheduling function: the MAC layer determines the radio resource to beused for announcing the discovery information received from the upperlayer. In addition, the AS layer has the function of generatingDiscovery PDU: the MAC layer builds the MAC PDU carrying the discoveryinformation and sends the MAC PDU to the physical layer for transmissionin the determined radio resource. No MAC header is added.

In the UE, the RRC protocol informs the discovery resource pools to MAC.RRC also informs allocated Type 2 resource for transmission to MAC.There is no need for a MAC header. The MAC header for discovery does notcomprise any fields based on which filtering on Layer 2 could beperformed. Discovery message filtering at the MAC level does not seem tosave processing or power compared to performing filtering at the upperlayers based on the ProSe UE and/or ProSe Application ID. The MACreceiver forwards all received discovery messages to upper layers. MACwill deliver only correctly received messages to upper layers.

In the following it is assumed that L1 indicates to MAC whether adiscovery message has been received correctly. Further, it is assumedthat the Upper Layers guarantee to deliver only valid discoveryinformation to the Access Stratum.

Prior art solutions for allocation of resources for discovery in D2Dsystems do not allow determining a resource pattern or a configurationsuitable for allocating resources in a manner that is suitable for therequested D2D service. Specifically, based on the informationtransmitted by the D2D capable device according to common signalingprocedures, the base station could allocate the transmission resourcesfor a too-short time period for allowing the UE to broadcast thecomplete discovery information. Consequently, the transmitting UE needsto request resources again, thereby leading to an increase of signalingoverhead into the LTE system.

Moreover, for example, information on the content of discoveryinformation is transparent to the Access Stratum (AS). Therefore, nodistinction is made in the Access Stratum between the various ProSeDirect Discovery models and types of ProSe Direct Discovery, and thebase station would not receive any information useful for determiningthe model of discovery transmission and the type of preferred procedurefor allocating discovery resources.

SUMMARY OF THE INVENTION

One exemplary embodiment provides a user equipment and a method forperforming allocation of resources in a D2D communication system. Aresource request message for allocation of resources for discoverytransmission including information on the amount of data to betransmitted and on discovery information is generated at the userequipment and transmitted to the base station.

The object of the invention is solved by the subject matter of theindependent claims. Advantageous embodiments are subject to thedependent claims.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same

BRIEF DESCRIPTION OF THE FIGURES

In the following the exemplary embodiments will be described in moredetail in reference to the attached figures and drawings. Similar orcorresponding details in the figures are marked with the same referencenumerals.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE;

FIG. 3 shows exemplary subframe boundaries on a downlink componentcarrier as defined for 3GPP LTE (Release 8/9);

FIG. 4 shows an exemplary downlink resource grid of a downlink slot asdefined for 3GPP LTE (Release 8/9);

FIGS. 5 and 6 show the 3GPP LTE-A (Release 10) Layer 2 structure withactivated carrier aggregation for the downlink and uplink, respectively;

FIG. 7 shows the structure of a MAC Control Element;

FIG. 8 is a schematic illustration showing the overlay (LTE) and theUnderlay (D2D) transmission and reception resources in D2D subframes;

FIG. 9 is a schematic illustration showing a system including D2Dcapable user equipments;

FIG. 10 shows a schematic representation of the PC5 interface fordevice-to-device direct discovery;

FIG. 11 shows a schematic representation of the Radio Protocol Stack forProSe Direct Discovery;

FIG. 12 is a diagram showing the IDLE and CONNECTED mode in thereception of discovery resources according to an exemplary example;

FIG. 13 is a flow chart illustrating the scheme for allocation ofresources for discovery transmission in a D2D communication system;

FIG. 14 illustrates schematically a D2D communication system including abase station and transmitting/receiving equipments according to anexemplary embodiment;

FIG. 15 illustrates a composition of a MAC Protocol Data Unit (PDU)according to an implementation of the scheduling method and systemaccording to the invention.

FIG. 16 is a schematic drawing illustrating the resource allocationwithin a discovery resource period.

DETAILED DESCRIPTION

The following paragraphs will describe various exemplary embodiments.For exemplary purposes only, most of the embodiments are outlined inrelation to a radio access scheme according to 3GPP LTE (Release 8/9)and LTE-A (Release 10/11/12) mobile communication systems, partlydiscussed in the Technical Background section above. It should be notedthat the exemplary embodiments may be advantageously used, for example,in a mobile communication system such as 3GPP LTE-A (Release 10/11/12)communication systems as described in the Technical Background sectionabove, but the exemplary embodiments are not limited to their use inthis particular exemplary communication network.

The term “direct link” used in the claims and in the description is tobe understood as a communication link (communication channel) betweentwo D2D user equipments, which allows the exchange of data directlywithout the involvement of the network. In other words, a communicationchannel is established between two user equipments in the communicationsystem, which are close enough for directly exchanging data, bypassingthe eNodeB (base station). This term is used in contrast with “LTE link”or “LTE (uplink) traffic”, which instead refers to data traffic betweenuser equipments managed by the eNodeB.

The term “transmitting user equipment” used in the claims and in thedescription is to be understood as a mobile device capable oftransmitting and receiving data. The adjective transmitting is onlymeant to clarify a temporary operation. The transmitting user equipmentin the following and for the purpose of discovery transmission can be anannouncing user equipment or a discovering user equipment (discoverer).The term is used in contrast to “receiving user equipment”, which refersto a mobile device temporarily performing the operation of receivingdata. The receiving user equipment in the following and for the purposeof discovery transmission can be a monitoring user equipment or a userequipment to be discovered (discoveree).

The term “discovery transmission” used in the claims and in thedescription is to be understood as transmission of a discoveryannouncement by a transmitting equipment or as a request indicatinginformation the transmitting equipment is interested to discover.

The term “discovery information” used in the claims and in thedescription is to be understood as information that the transmittinguser equipment transmits to the base station to the purpose of resourceallocation for discovery transmission. Discovery information includesany information which can be used, together with the amount of data tobe transmitted, by the base station in order to effectively allocateresources for discovery transmission.

In the following, several examples will be explained in detail. Theexplanations should not be understood as limiting the invention, but asa mere exemplary embodiments to better understand the invention. Askilled person should be aware that the general principles as laid outin the claims can be applied to different scenarios and in ways that arenot explicitly described herein. Correspondingly, the following scenarioassumed for explanatory purposes of the various embodiments shall not belimiting as such.

An exemplary aspect of the invention is related to the discoveryprocedure for Device-to-Device communication, for example for proximityservices (ProSe).

An eNB may provide D2D reception discovery resources in Systeminformation Broadcast (SIB). These resources may cover resources usedfor D2D transmission in the cell in which a transmitting user equipmentis registered (current cell), as well as resources used in neighborcells. A SIB in a Device-to-Device communication system is the broadcastof information pertaining to D2D in the underlay network. The network,i.e., eNB or base station, may broadcast information related to D2D(called D2D SIB(s)) in separate System Information Blocks (SIB). Same ordifferent SIBs may indicate the D2D resources for Receiving Inter-cellDiscovery messages.

For D2D capable UEs which are in the coverage of a network, i.e.,referred to as in-coverage UEs, the discovery procedure can bedistinguished between idle mode UEs and connected mode UEs, i.e., UEshaving established a RRC connection to the network. The two modes willbe described below in connection with FIG. 12.

For user equipments in IDLE 400 the UE reads D2D related SIB informationprovided by the base station or by the network, which may be, forinstance information on whether the base station respectively whetherthis cell supports D2D or not (401, 402). The base station may furtherprovide a Type 1 transmission resource pool in the System informationBroadcast 410, in which the resources are allocated independently fromthe UE. The UEs that are authorized for D2D Discovery use the resourcesin the transmission pool in IDLE. In other words, the UE may choose froma transmission resource pool from the available resources and starttransmitting a discovery message.

Alternatively, if no information on the transmission resource pool isprovided by the base station (401), then the UE may switch its status tothe connected mode (402) and then request D2D resources for discoverytransmission. More in particular the D2D-enabled UE will initiate theRRC connection establishment procedure in order to move to RRC connectedmode and further indicate the request for resources for the transmissionof discovery announcements. At this point, the base station may send aresponse to the request of the UE setting the procedure for allocatingresources. The base station may choose now to allocate resources on anon-UE-specific basis (type 1 procedure). Allocation of resources inconnected mode may be done by exchanging RRC messages (431). Onceallocation of resources is completed, the UE can start transmitting thediscovery message (441).

According to a further alternative, the base station may use anallocation procedure, where resources for announcing of discoveryinformation are allocated on a per UE-specific basis (type 2 procedure).Accordingly, the base station indicates a transmission resource pool butdoes not allocate transmission resources specific to the userequipments. Instead, the UE autonomously selects radio resource(s) fromthe indicated resource pool and announces discovery information (430).

In the connected mode, a UE authorized to perform D2D discoverytransmission sends to the base station requests to establish D2Ddiscovery transmissions. Specifically, the UE requests to the basestation configuration of discovery transmission resources (430, 431).Besides the request for configuration of discovery transmissionresources, the UE may also transmit to the base station furtherinformation. The further information may include an indication of thetype of discovery procedures the UE wishes to use for discoverytransmission. In accordance with the request from the UE, the basestation allocates resources according to a type 1 or a type 2 procedureas described above (440, 441).

FIG. 13 is a flow chart illustrating the scheme for allocation ofresources for discovery transmission in a D2D communication systemaccording to the invention as described in connection with FIG. 12.Firstly, the base station determines at step S00 whether the UE isauthorized for D2D discovery. Although this step is shown in thisexample at the beginning of the discovery resource allocation procedure,step S00 does not have to be necessarily part of the D2D discoveryresource allocation procedure and it may be done at an earlier point oftime. Alternatively, determination whether the UE is authorized for D2Ddiscovery can be performed within the resource allocation procedure. Ifthe UE is not authorized for D2D discovery, the procedure fortransmitting discovery information is stopped at step S07. In step S01the transmitting UE is in an idle mode, for example in an RRC_IDLE mode.The transmitting UE reads D2D related SIB information to determinewhether the base station or the cell in which the transmitting userequipment is logged. Specifically, the UE determines whether the basestation provides the SIB with a transmission resource pool (step S02).If the type 1 transmission resource pool is provided by the basestation, it may be determined, whether the transmitting UE is authorizedfor performing D2D discovery, in the case this was not done before.Thereafter, the transmitting UE uses the resources in the transmissionresource pool for performing a type 1 discovery transmission (step S08).

If the base station does not provide a transmission resource pool fordiscovery transmission according to a type 1 procedure, the UE switchesin step S03 to a RRC_CONNECTED mode. Switching to RRC_CONNECTEDcorresponds to a new RRC connection establishment trigger. In otherwords, the RRC establishment procedure is triggered by Access Stratumdue to the absence of D2D Type 1 transmission resource pool information.Therefore, according to one embodiment a new establishment cause valueis introduced in the RRC connection request message, i.e.,establishmentCause field in RRCConnectionRequest message (see section5.3.3 of TS36.331). This new establishmentCause value indicates that UEwants to establish RRC connection for the purpose of D2D oralternatively for the purpose of D2D discovery. Next in step S04 the UEsends to the base station a resource request message for allocation ofresources for discovery transmission, the resource request messageincluding information on the amount of data to be transmitted. Theresource request message may also include further information accordingto which the base station can decide how may resources to allocate forthe discovery transmission and for how long said resources should bemade available to the transmitting user equipment. The furtherinformation as well as the effects and advantages associated theretowill be explained later in relation to a further exemplary embodiment.The radio resource request message can be according to one embodimentalso sent as part of the RRC connection establishment procedure. In theaffirmative case, the base station can decide, based on the informationwithin the resource request message or based on other parameters, suchas the availability of resources, or on the collision rate, whether theallocation of resources should be carried out according a UE independent(type 1) or UE-specific (type 2) allocation procedure. If in step S05the base station decides for a type 1 resource allocation procedure, theprocess jumps to step S08. Alternatively, if the base station decidesfor a type 2 resource allocation procedure, the transmitting UE requestsallocation of resources according to a UE-specific procedure (type 2procedure). Once the resources for discovery transmission are allocated,the transmitting UE proceeds with discovery transmission

FIG. 14 illustrates schematically a D2D communication system accordingto the invention including a base station 510 and ProSe capable UEs ortransmitting/receiving equipment 500 according to an exemplaryembodiment. For explanation proposes in the following we will refer tothe UE as transmitting UE or simply UE. It has however to be understoodthat such device is clearly also capable of receiving data in the D2Dcommunication system on a standard LTE channel and on a direct link datachannel.

The UE 500 includes a generating unit 570, which is adapted to generatea resource request message for allocation of resources for discoverytransmission. The resource request message includes information on theamount of data needed for transmitting discovery announcements ormessages. The value on the amount of data to be transmitted is thenoutput to a signalling transmitting unit 560 and then transmitted to thebase station 510. Based on the value on the amount of data to betransmitted, the base station 510 can allocate the exact amount ofresources needed by the UE for transmitting the discovery announcement.In addition to information on the data amount to be transmitted, thegenerating unit may also generate discovery indication. Discoveryindication may include any information relative to the transmission ofthe discovery message and is used by the base station 510 to allocatethe resources and the time slots for discovery transmission in order toincrease the efficiency of the discovery transmission. The discoveryindication and the information on the data amount to be transmitted aremultiplexed at a multiplexing unit (not shown) into the resource requestmessage. The transmitting unit 560 then transmits the generated resourcerequest message to the base station.

The UE further includes a reception unit or receiving unit 540 adaptedto receive a message from the base station allocating the resources fordiscovery transmission. In addition, the UE may optionally include adelay unit 560, a control unit 590 and a timing unit 550. These unitswill be described in detail with reference to a further exemplaryembodiment.

The discovery indication may be an indication on discovery and mayinclude at least one of a type of discovery service, a duration of thediscovery transmission, a number of discovery transmissions, a preferredresource allocation pattern and a preferred type of discoverytransmission procedure. This list is only for explicative purposes andit does not have to be understood as being exhaustive or limiting. Anyother information that can be used by the base station 510 in order toperform allocation of resources may be used in addition to or instead ofthe information pieces listed above.

Additional information indicating the type of discovery service may beused by the base station for prioritizing assignment of resources to theUE. The UE may need to broadcast a discovery message concerning, forexample, public safety. This could be the case if an accident occurredand a section of a road is dangerous or impracticable. Any delay intransmission of such discovery message may have some serious consequenceon the security of the users and in general of the traffic participants.In this case the generating section may include in the resource requestmessage information on the type of discovery service, which indicatesthat the discovery is for public safety. According to this additionalinformation the base station may give a higher priority to the discoverymessage. As an example, based on the additional information on the typeof discovery service, the base station may decide to allocate resourcesfor discovery transmission using a type 2 procedure. As alreadydescribed above, such procedure allows to allocate resources in a mannerspecific to the UE sending the request. Such procedure has the advantagethat there will be no collision among different UEs, thereby increasingdiscovery transmission efficiency. In addition, the information on thetype of discovery service may be used by the base station for decidingthe size of the resources to be allocated in a defined timeframe.

As a further embodiment of the invention, the discovery indication mayinclude the number of discovery transmissions to be carried out by theUE or the duration of the discovery transmission. To this end, the UEmay include a timing unit 550 adapted to calculate the timing and thenumber of discovery transmissions. The timing unit is however notnecessary and the timing function may be carried out by any other unitin the UE. Alternatively, the timings may be fixed and timinginformation may be available to the UE. The timing information or theinformation on the number of discovery transmissions may be used by thebase station 510 in order to allocate the resources for discoverytransmission for the necessary time window. This allows preventing theUE 500 from repeatedly sending to the base station a request forallocating resources discovery transmission, thereby reducing signalingoverhead.

Another example of discovery indication may be information on whetherthe discovery type is model A or model B, which have been described indetail in the introductory portion.

The transmitting user equipment 500 may include in the resource requestmessage a type of discovery transmission procedure. The type ofdiscovery transmission procedure includes a first procedure, wherein theallocation of resources for discovery transmission is independent fromthe transmitting user equipment. The first procedure corresponds to thetype 1 allocation procedure described in the introductory portion. Inaddition or alternatively the type of discovery transmission procedureincludes a second procedure, wherein the allocation of resources fordiscovery transmission is specific for the transmitting user equipment.The second procedure corresponds to the type 2 allocation proceduredescribed in the introductory portion.

According to an exemplary embodiment of the invention, the resources ofdiscovery transmission are requested using the RRC protocol.Accordingly, the resource request message is a radio resource controlmessage. A new RRC message is introduced which carries the resourcerequest information, e.g., ProseDiscoveryIndication message. In responseto this request message the base station will send a new RRC message,e.g., DiscoveryResourceConfig message, containing the resourceconfiguration for D2D discovery announcements, i.e., either thetransmission resource pool information (type 1) or the dedicatedresource allocation info (type 2).

Alternatively, the request for allocating resources for discoverytransmission can be implemented in a SR/BSR signaling procedure for D2Dcommunication, by using a common signaling scheme for discovery and datatransmission.

A scheduling request (SR) may be transmitted via resources of the PUCCHallocated by the base station, i.e., also referred to as dedicatedscheduling request (D-SR). A dedicated scheduling request is usually onebit long, and corresponding periodic PUCCH resources allow transmittingthe scheduling request but are not sufficient for transmitting furtherdata such as the buffer status report or actual data of the transmissionbuffer. As described in the technical background section, in LTE ascheduling request is triggered for the case that a buffer status reporthas been triggered but there are no PUSCH resources available for thetransmission of the buffer status report. In other words the purpose ofthe scheduling request is to ask the base station for the allocation ofPUSCH resources so that UE could transmit the buffer status report,which in turn enables the base station to allocate adequate resourcesfor the transmission of the uplink data.

A D2D enabled transmitting UE transmits a scheduling request (SR) eitheron the PUCCH (D-SR) or on RACH when there is a buffer status reporttriggered for D2D bearers, e.g., when new data arrives for a D2D bearer.This scheduling request is transmitted in a regular LTE uplinktime/frequency resource, i.e., not on a time/frequency resource reservedfor D2D. Upon receiving this scheduling request the base station 510will allocate PUSCH resources to the D2D transmitting UE. The D2Dtransmitting UE will transmit in turn the D2D related buffer statusinformation within this PUSCH resources as described already above.Based on the detailed buffer status information, the base station 510will allocate D2D time/frequency resources for the D2D datacommunication.

As mentioned above the second uplink grant/resource allocation, i.e.,upon having received the D2D related buffer status information, may usea different resource allocation format/DCI, e.g., addressed to a D2DRNTI.

FIG. 15 describes a composition of a MAC Protocol Data Unit (PDU)according to an implementation of the above-described scheduling scheme.The MAC Protocol Data Unit referred to in the buffer status reportingprocedure according to the scheduling method described aboveincorporates a control element for performing D2D related signaling.Preferably, the scheduling information for D2D communication may be aD2D dedicated Buffer Status Report, which may be implemented by a MACcontrol element for D2D communication. Accordingly, the MAC ProtocolData Unit transmitted on the PUSCH may include, besides the MAC controlelements, such as MAC BSR/PHR CEs (indicated in FIG. 11 as MAC CE1 andMAC CE2), used for performing scheduling in uplink LTE traffic, also oneor more D2D MAC control element, which will be used for performingscheduling of the resources for transmitting data from the transmittinguser equipment to the receiving user equipment on the direct linkchannel.

The D2D MAC control element in the MAC PDU may be further associated toan identification number. Said identification number may be, forexample, a reserved logical channel ID, which may be stored in theheader of the MAC PDU, i.e., MAC subheader. Advantageously, theidentification number may be stored in the R/R/E/LCID subheadercorresponding to the D2D MAC CE. Accordingly, the base station will beable to distinguish which buffer status report in the MAC PDU has to beused for scheduling procedures of D2D data transmission on the directlink connection or for scheduling LTE cellular uplink traffic. Thislogical channel ID may be one of the reserved logical channel IDs(LCIDs).

According to an exemplary embodiment, if the UE is authorized totransmit discovery messages, it sends a scheduling request (SR) and D2DBuffer Status Report (BSR) for requesting radio resources or forconfiguring discovery transmission. The discovery scheduling request istransmitted to the base station on an uplink data channel for datatransmission. As an example, the discovery scheduling request may betransmitted within a MAC control element for direct link communication.MAC control element for direct link communication may be a D2D BSR MACControl Element in the LTE MAC PDU.

According to an exemplary embodiment of the invention, the D2D BSR MACControl Element may comprise an identification value, such as a flag,which identifies whether the transmission is discovery transmission ordata transmission. If the flag indicates discovery, the reported amountof bytes corresponds to the discovery message size. On the other hand,if the flag indicates that the D2D BSR MAC Control Element is forrequesting allocation for D2D data transmission, the reported amount ofbytes corresponds to the data of the D2D bearers.

In addition or alternatively, if the flag indicates that the D2D BSR MACCE is for discovery transmission, the latter may contain additionalinformation as already explained before, like a suggested pattern,information on whether the discovery message is public safety ornon-public safety, or the preference of the UE for Type1/Type2allocation.

Specifically, information that the discovery transmission procedure isof type 1 communicates to the base station that the allocation ofresources for discovery transmission is independent from thetransmitting user equipment. The type 1 transmission procedure is alsoindicated as first procedure.

Specifically, information that the discovery transmission procedure isof type 2 communicates to the base station that the allocation ofresources for discovery transmission is specific for the transmittinguser equipment. The type 2 transmission procedure is also indicated assecond procedure.

Discovery transmission may be stopped by the base station either afterthe time indicated in the resource request message transmitted by the UEor on its own motion, in order to manage the resources available in thecell. Alternatively, the base station may interrupt the discoverytransmission because it does not know that the UE still wants totransmit discovery messages. This could happen, for example, if the UEis transmitting discovery announcements according to Mode B, describedbefore. In this case, the UE periodically sends discovery announcementsincluding information on what the UE is interested to discover and waitsuntil a discoveree positively answers to the announcement request.

As an example of transmission interruption, the base station maydeconfigure the allocated resources for discovery transmission(announcement). Alternatively, the base station may release the RRCconnection of a D2D UE even though the D2D UE still intends to continuewith the discovery announcements.

In an exemplary embodiment of the invention, the receiving unit 540 ofthe UE 500 may receive from the base station 510 an interrupt messagefor interrupting discovery transmission. This can occur when the basestation deconfigures resources or releases the RRC connection. Thus, theinterrupt message includes at least one of a de-configuration messagefor de-configuring the allocated resources for discovery transmission ora release message for releasing a radio resource control connection.

According to standard communication schemes, the UE would re-start thediscovery transmission procedure right after the resources aredeconfigured or the RCC connection has been released by the basestation. A new request for an RRC connection or a request for discoverytransmission resources is thus transmitted to the base station. However,if the base station deconfigures the transmission resources because thelatter are not available anymore, transmission of a new request forallocation of resources will merely increase the signalling overhead,without successfully obtaining for the UE an allocation of resources. Inorder to avoid that, the UE re-transmits a request for allocation ofresources for D2D discovery announcement immediately after theconnection has been released or the resources have been deconfigured; inan exemplary embodiment a prohibit mechanism is introduced whichprevents UE from requesting discovery resources for a specified timeafter the resources have been deconfigured. To this end, the basestation 510 may send, along with a deconfiguration message, a timervalue to the UE. The receiving unit 540 sends the timer value to thedelay unit 580, and the delay unit 580 controls the transmitting unit560 and delays the transmission according to the received timer value.

The timer value may be signalled by the base station 510 within aninterrupt message resource deconfiguration message or within the messagefor releasing the RRC connection. Alternatively, the timer value may bespecified at the time the resources for discovery transmission wereallocated. For example, the timer value may be specified in the messagetransmitted by the base station for granting the resources for discoverytransmission. Thus, information on the predetermined time for which thetransmission of a new resource request message is inhibited may beincluded in the received de-configuration message or in the resourceconfiguration message.

As an alternative or in addition to the timer value, the base stationmay include within the RRC connection release message Type 1transmission resource pool information. Accordingly, after interruptionof transmission by the base station, the UE may independently chooseresources for discovery transmission from the transmission resource pooland re-start discovery transmission independently from the base station.

In another exemplary embodiment of the invention, the transmitting userequipment 500 which has been configured for Type 1 discoverytransmission in RRC_CONNECTED, —in the case, for example that the basestation provided transmission resource pool information to thetransmitting user equipment in response to the radio resource request—isallowed to continue sending discovery announcements also in RRC_IDLEmode. Type 1 discovery resources are allocated on a non-UE-specificbasis even for the case that the allocation is realized when UE is inRRC_CONNECTED mode. Therefore, the allocated resource can be used byother UEs even if the UE does not explicitly request the release of theallocated resources. Therefore, Type 1 discovery resources allocatedwhen UE is RRC_CONNECTED can be used also when UE has transited toRRC_IDLE. For example, the UE is allowed to continue sending D2Ddiscovery announcements upon having been sent to RRC_IDLE mode until thevalidity timer or timer value expired. More specifically, the validitytimer started in RRC_CONNECTED should be continued even if UE entersRRC_IDLE. Accordingly, the UE is authorized to do discoveryannouncements for a certain ProSe Application for the duration of thevalidity timer. The validity timer may be assigned during theauthorization procedure. Alternatively the base station may indicate inthe RRCConnectionRelease message for how long the UE is allowed tocontinue discovery announcements according to Type 1 resource allocationprocedure in RRC_IDLE mode.

In another exemplary embodiment of the invention, the transmitting userequipment 500 generates status information including a continuationmessage, or keep or maintain message for requesting the base station 510to maintain the resources allocated for discovery transmission, and/or astop message indicating that the allocated resources for discoverytransmission can be de-configured. The status information may betransmitted to the base station at predefined time intervals.

For example, the UE in RRC_CONNECTED may send the keep message to thebase station indicating that it wants to continue discovery announcementor maintain the allocated transmission resources for discoveryannouncement. Thus, the keep message may be sent independently to thebase station, for example using the RRC protocol. AProseDiscoveryIndication message may be, for instance, sent again inorder to indicate that UE wants to continue with discoveryannouncements. Alternatively, the keep message may be conveyed by a MACcontrol element, such as for instance the D2D MAC control elementdescribed in connection with FIG. 15. The keep message may be sent tothe base station at predetermined time intervals, which can be chosen tobe shorter than the time interval after which the base stationdeconfigures transmission resources. Determination of the time intervalmay be done at the timing unit 550. The timing unit may output thedetermined time interval to the control unit 590. Subsequently, thecontrol unit 590 may instruct the generating unit to generate the keepmessage. The generating unit 570 may generate the keep message as anindependent message to be transmitted on the RRC protocol, or it mayinclude the keep message in a MAC CE as described above. The generatedkeep message or the MAC CE including keep information is then output tothe transmitting unit and transmitted to the base station.Alternatively, the timing unit may output the determined timeinformation directly to the transmitting section 560.

In addition or alternatively to the keep message, the UE may send a stopmessage or indication to the base station. The stop message indicatesthat the UE does not need transmission resources for discoveryannouncement anymore. Similarly to the keep message, it may be sentindependently to the base station using the RRC protocol, such as aProseDiscoveryIndication message with zero buffer size or predefinedvalues, or it may be included in a MAC control element, such as forinstance the D2D MAC control element described in connection with FIG.15. Generation of the stop message can be instructed by the control unit590 once the control unit decides that discovery transmission can beinterrupted. The higher layer within the UE, e.g., Proximity applicationlayer, may indicate to the access stratum layer within the UE togenerate the stop message. Upon reception of the stop indication, thebase station deconfigures the transmission resource for discoveryannouncements or moves the UE to RRC_IDLE. The above-describedconfiguration can be advantageously used in particular if the UE istransmitting discovery announcements according to model B. By sendingthe keep message, the UE can prevent the base station from deconfiguringtransmission resources for discovery announcements or to bring the UE toRRC_IDLE mode, while the UE actually still intends to periodicallytransmit discovery announcements. Similarly, by sending the stopmessage, the UE can inform the base station that transmission resourcesfor discovery announcements can be deconfigured or, more generally thatthe discovery transmission can be interrupted/stopped. This prevents thebase station from keeping configuration of resources unnecessary long.Accordingly, the configuration described above allows reducing signalingoverhead, by preventing the base station to interrupt discoverytransmission before time and thus preventing the UE to re-send a newresource request message. Further, the transmission of a stop message bythe UE allows the base station to free transmission resources, which canbe used for fulfilling allocation requests from other UEs in the cell,thereby increasing the efficiency of the system.

The base station 510 for use in the direct link communication systemdescribed above may comprise a receiving unit (not shown) adapted toreceive from the transmitting user equipment 500 a resource requestmessage for allocation of resources for discovery transmission. The basestation 510 may further include a generating unit (not shown) adapted togenerate, in response to the received resource request message, aresource configuration message allocating the requested resources fordiscovery transmission, and a transmitting unit (not shown) adapted totransmit the generated resource configuration message to the UE.

According to an exemplary embodiment of the invention, the base station510 may further include a deciding section (not shown). The decidingsection may be in charge of managing the allocation of resources and ofdeciding the type of transmission protocol and allocation resourcepattern to be used by the UE for transmission of discoveryannouncements. For example, the resource request message transmitted bythe UE may include ProSe discovery indication, such as the type ofdiscovery procedure or the estimated duration of the transmission or thenumber of the transmission. Upon reception of said resource requestmessage, the base station may determine the more appropriate timing forreleasing the transmission resources of D2D discovery announcements. Aschematic drawing of the resource allocation within a discovery resourceperiod in shown in FIG. 16.

In addition or alternatively, the deciding section may be adapted toread the received resource request message and based thereon decidewhether resources for discovery transmission are to be allocatedaccording to a type 1 or according to a type 2 procedure. Further, thedeciding section may be adapted to read an identification value includedin the D2D MAC CE identifying whether the transmission is discoverytransmission or data transmission. Based on the identification value,the deciding section may be adapted to decide whether to allocateresources for discovery transmission or for data transmission on adirect link.

According to an exemplary embodiment of the invention, a transmittinguser equipment is given for transmitting data to a receiving userequipment over a direct link connection in a communication system. Thetransmitting user equipment is adapted to request resources fordiscovery transmission in the communication system and comprises agenerating unit configured to generate a resource request message forallocation of resources for discovery transmission. The resource requestmessage includes information on the amount of data to be transmitted andon discovery indication. The transmitting user equipment may furtherinclude a transmitting unit configured to transmit to a base station thegenerated resource request message, and a receiving unit adapted toreceive from the base station a resource configuration messageallocating the requested resources for discovery transmission.

According to a further embodiment, the discovery indication includes atleast one of a type of discovery service, a duration of the discoverytransmission, a number of discovery transmissions, a preferred resourceallocation pattern and a preferred type of discovery transmissionprocedure.

The resource request message may be a radio resource control message ormay be discovery scheduling information transmitted to the base stationon an uplink data channel for data transmission.

The discovery scheduling information may be, for example, transmittedwithin a MAC control element for direct link communication. In additionor alternatively, the MAC control element may comprise an identificationvalue identifying whether the transmission is discovery transmission ordata transmission.

According to an exemplary embodiment of the invention, the type ofdiscovery transmission procedure includes a first procedure, wherein theallocation of resources for discovery transmission is independent fromthe transmitting user equipment.

According to a further exemplary embodiment of the invention, the typeof discovery transmission procedure includes a second procedure, whereinthe allocation of resources for discovery transmission is specific forthe transmitting user equipment.

In the transmitting user equipment the receiving unit may be adapted toreceive from the base station an interrupt message for interruptingdiscovery transmission. The transmitting user equipment may also furtherinclude a delaying unit adapted to inhibit transmission of a newresource request message for allocation of resources for discoverytransmission to the base station for a predefined time. The interruptmessage may include at least one of a de-configuration message forde-configuring the allocated resources for discovery transmission and arelease message for releasing a radio resource control connection.Further, information on the predefined time may be included in thereceived de-configuration message or in the resource configurationmessage.

In the transmitting user equipment the generating unit may be furtheradapted to generate status information including a continuation messagefor requesting the base station to maintain the resources allocated fordiscovery transmission, or a stop message indicating that the allocatedresources for discovery transmission can be de-configured. Thetransmitting unit may be further adapted to transmit the statusinformation to the base station at predefined time intervals. The statusinformation may be included in a MAC control element, preferably the MACcontrol element for direct link transmission.

According to a further exemplary embodiment of the invention, a basestation is given for use in a direct link communication system. The basestation may be adapted to assign resources for discovery transmission inthe communication system and may comprise a receiving unit adapted toreceive from a transmitting user equipment a resource request messagefor allocation of resources for discovery transmission. The base stationmay further include a generating unit adapted to generate, in responseto the received resource request message, a resource configurationmessage allocating the requested resources for discovery transmission,and a transmitting unit adapted to transmit the generated resourceconfiguration message.

In an exemplary embodiment of the invention, the resource configurationmessage may be a radio resource control message. Alternatively, theresource configuration message may be transmitted on the downlinkcontrol channel (PDCCH) for discovery transmission on the uplink datachannel.

The base station for use in a direct link communication system mayfurther include a deciding section adapted to read the received resourcerequest message and based thereon decide whether resources for discoverytransmission are to be allocated according to a first or to a secondprocedure.

In an exemplary embodiment of the invention, the grant of resourcesmessage may include an identification value identifying whether thegrant of resources message allocates resources for discoverytransmission or for data transmission.

An exemplary embodiment of the invention describes a communicationmethod for requesting resources for discovery transmission by atransmitting user equipment in a communication system. The methodcomprises the steps of generating, at a generating unit, a resourcerequest message for allocation of resources for discovery transmission.The resource request message may include information on the amount ofdata to be transmitted and discovery indication. The method furthercomprises the steps of transmitting, at a transmitting unit, to a basestation the generated resource request message, and receiving, at areceiving unit, from the base station a resource configuration messageallocating the requested resources for discovery transmission.

In the communication method, the discovery indication may include atleast one of a type of discovery service, a duration of the discoverytransmission, a number of discovery transmissions, a resource allocationpattern and a type of discovery transmission procedure.

In the communication method, the resource request message may be a radioresource control message or discovery scheduling information transmittedto the base station on an uplink data channel for data transmission.

According to an exemplary embodiment of the invention, the discoveryscheduling information may be transmitted within a MAC control elementfor direct link communication. The MAC control element may comprise anidentification value identifying whether the transmission is discoverytransmission or data transmission.

The type of discovery transmission procedure includes a first procedure,wherein the allocation of resources for discovery transmission isindependent from the transmitting user equipment. Alternatively, thetype of discovery transmission procedure includes a second procedure,wherein the allocation of resources for discovery transmission isspecific for the transmitting user equipment.

According to an exemplary embodiment of the invention, the communicationmethod may further comprise the steps of receiving, at the receivingunit, from the base station an interrupt message for interruptingdiscovery transmission, and inhibiting, at a delaying unit, transmissionof a new resource request message for allocation of resources fordiscovery transmission to the base station for a predefined time.

In the communication method according to an exemplary embodiment of theinvention, the interrupt message may include at least one of ade-configuration message for de-configuring the allocated resources fordiscovery transmission and a release message for releasing a radioresource control connection.

In the communication method according to an exemplary embodiment of theinvention, information on the predefined time may be included in thereceived de-configuration message or in the resource configurationmessage.

The communication method according to an exemplary embodiment of theinvention may further comprise the steps of, at the generating unit,generating status information. The status information may include acontinuation message for requesting the base station to maintain theresources allocated for discovery transmission, or a stop messageindicating that the allocated resources for discovery transmission canbe de-configured. The method further includes the step of transmitting,at the transmitting unit, the status information to the base station atpredefined time intervals.

In the communication method according to an exemplary embodiment, thestatus information may be included in a MAC control element, preferablythe MAC control element for direct link transmission.

Hardware and Software Implementation of the Invention

Another aspect of the invention relates to the implementation of theabove-described various embodiments and aspects using hardware andsoftware. In this connection the invention provides a user equipment(mobile terminal) and a eNodeB (base station). The user equipment isadapted to perform the methods described herein. Furthermore, the eNodeBcomprises means that enable the eNodeB to evaluate the IPMI set qualityof respective user equipments from the IPMI set quality informationreceived from the user equipments, and to consider the IPMI set qualityof the different user equipments in the scheduling of the different userequipments by its scheduler.

It is further recognized that the various embodiments of the inventionmay be implemented or performed using computing devices (processors). Acomputing device or processor may for example be general purposeprocessors, digital signal processors (DSP), application-specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments of the invention may individually or in arbitrarycombination be subject matter to another invention.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

1. An integrated circuit configured to control operation of a basestation, the integrated circuit comprising: reception circuitry, which,in operation, receives from a communication apparatus a request messageincluding a resource request, the resource request indicating a numberof discovery messages used for a discovery announcement; andtransmission circuitry, which is coupled to the reception circuitry andwhich, in response to the request message, transmits to thecommunication apparatus a resource scheduling message indicating whichone of dedicated resources assigned to the communication apparatus andnon-dedicated resources assigned to non-specific communicationapparatuses are used for the discovery announcement; wherein, inresponse to the resource scheduling message, the communication apparatustransmits the discovery announcement using the dedicated resources orthe non-dedicated resources.
 2. The integrated circuit according toclaim 1, wherein the reception circuitry, in operation, receives a stopmessage indicating that resources for the discovery announcement are nolonger required.
 3. The integrated circuit according to claim 2, whereinthe stop message causes the assigned dedicated resources to bedeconfigured.
 4. The integrated circuit according to claim 1, whereinthe reception circuitry, in operation, receives the request messageincluding the resource request when the communication apparatus isallowed to transmit the discovery announcement.
 5. The integratedcircuit according to claim 1, wherein the resource request includesinformation on an amount of data transmitted in the discoveryannouncement.
 6. The integrated circuit according to claim 1, whereinthe request message is a radio resource control (RRC) message andfurther includes information on a type of the discovery messages.
 7. Theintegrated circuit according to claim 1, wherein the dedicated resourcesand the non-dedicated resources are a plurality of time or frequencyresources.
 8. The integrated circuit according to claim 1, wherein thediscovery announcement is transmitted from the communication apparatusin order to discover an existence of another communication apparatus.